In an optical pickup device such as, for instance, a photoelectromagnetic disk, used for recording/playing back data in or deleting data from an optical recording medium, a semiconductor laser chip is used as laser light source.
Generally in case of a light flux outputted from a semiconductor laser chip, an angle in which the beam extends in the direction parallel to an active layer of a chip in the semiconductor laser chip is different from that in the direction vertical to the active layer of the chip in the semiconductor laser chip, and for this reason the cross section thereof is oval.
If a laser beam having an oval cross section is focused as it is onto an optical recording medium, such troubles as decrease in the recording density occur, so that adjustment is executed by using a beam shaping element so that a cross section of a flux outputted from the semiconductor laser chip will become oval.
FIG. 25 is a drawing illustrating a key section of an optical system in a conventional type of optical pickup device.
In this figure, laser light outputted from a semiconductor chip 1 is converted to parallel light by a coupling lens 2, goes into on a surface 3a of a beam shaping prism 3, and refracts on the surface 3a with the beam form shaped to a substantially oval form. Then the laser light subjected to beam shaping goes out from a face 3b of the beam shaping prism 3 into a beam splitter 4.
Of the laser light going into the beam splitter 4, a portion thereof which transmitted a face 4a for light separation is deflected by a deflection prism 5, guided to a object lens 6, and focused onto an optical recording medium 7 by the object lens 6.
The reflected light from the optical recording medium 7 is converted by the object lens 6 to substantially parallel light, reflected on the deflection prism 5, and is entered into the beam splitter 4. Then, of the reflected light going into the beam splitter 4, a portion thereof reflected on the light separating surface 4a of the beam splitter 4 is guided to an light detection system.
In this light detection system, reflected light from the optical recording medium 7 transmits a 1/2 waveform plate L with the polarization face turned by 45.degree., and is focused in the state by a focusing lens 8 and entered into the polarized beam splitter 9, and the p polarized portion which transmitted a face 9a for light separation of this polarized beam splitter 9 is received by a light receiving element 10, while the s polarized portion reflected on the face 9a for light separation is received by a light receiving element 11.
Also in this case, the beam shaping prism 3 to execute beam shaping for laser light outputted from the semiconductor chip 1 is adhered to the beam splitter 4 to separate the reflected light from the optical recording medium 7 from the source light, so that the two components can be treated as a single optical element 12. By using this optical element 12, easiness to assemble the device can be improved.
FIG. 26 indicates another example of an optical pickup device based the conventional configuration.
Namely, this optical pickup device emits laser light from a semiconductor laser 101A and converts the emitted light to parallel light through a coupling lens 102A. Then the light is passed through a beam shaping prism 103A to shape a light flux cross section of the laser light to a circular form.
Generally a light flux cross section of light emitted from a semiconductor laser chip is narrow in the direction parallel to an active layer of the chip and wide in the direction vertical to the inactive layer, so a form of the cross section is generally oval. If a laser spot on an optical disk is oval, various trouble occur, so a cross section of laser light is adjusted to a circular one.
The laser light shaped as described above is guided via a beam splitting element 104A to the optical disk side. Then, the laser light is focused by an object lens and irradiated onto an optical disk.
Also the reflected light from the optical disk is returned to the light splitting element 104A. All of a portion of the reflected light from the optical disk passes through the beam splitting element 104A, and is guided to a light detection system.
FIG. 27 is a drawing illustrating other example of configuration of an optical pickup device.
In this case of optical pickup device, laser light emitted from the semiconductor laser 101A is converted by the coupling lens 105A to parallel light, and at the same time a light flux cross section of the laser light is shaped to a circular one. Namely the hatched section in this figure indicates an extension of a oval light flux emitted from the semiconductor 101A in the direction of major axis thereof, and a diameter of the coupling lens 105A in the direction is narrower than the extension. Because of this feature, an outer peripheral section of the light flux in the direction of major axis thereof is cut off, and the light flux cross section becomes substantially circular after the parallel flux passed through the coupling lens 105A.
However, there are the following disadvantages in the conventional types of device as described above.
In the case shown in FIG. 25, as the beam shaping prism 3 and the beam splitter 4 are adhere to each other to make up the optical element 12, a number of optical parts becomes larger, which is disadvantageous.
Also in case of the configuration shown in FIG. 26, a number of optical parts such as the coupling lens 102A, beam shaping prism 103A, and beam splitting element 104A are necessary, which disadvantageously results in high production cost of the device.
Also in case of the configuration shown in FIG. 27, as the beam shaping prism 103A is not necessary, a number of parts can be reduced, but an outer peripheral section of the light flux in the direction of major axis thereof is cut off to shape the oval light flux, use efficiency of the light emitted from the semiconductor laser 101A disadvantageously drops.